Integrated in silico and experimental assessment of disease relevance of PCDH19 missense variants.

PCDH19 is a nonclustered protocadherin molecule involved in axon bundling, synapse function, and transcriptional coregulation. Pathogenic variants in PCDH19 cause infantile-onset epilepsy known as PCDH19-clustering epilepsy or PCDH19-CE. Recent advances in DNA-sequencing technologies have led to a significant increase in the number of reported PCDH19-CE variants, many of uncertain significance. We aimed to determine the best approaches for assessing the disease relevance of missense variants in PCDH19. The application of the American College of Medical Genetics and Association for Molecular Pathology (ACMG-AMP) guidelines was only 50% accurate. Using a training set of 322 known benign or pathogenic missense variants, we identified MutPred2, MutationAssessor, and GPP as the best performing in silico tools. We generated a protein structural model of the extracellular domain and assessed 24 missense variants. We also assessed 24 variants using an in vitro reporter assay. A combination of these tools was 93% accurate in assessing known pathogenic and benign PCDH19 variants. We increased the accuracy of the ACMG-AMP classification of 45 PCDH19 variants from 50% to 94%, using these tools. In summary, we have developed a robust toolbox for the assessment of PCDH19 variant pathogenicity to improve the accuracy of PCDH19-CE variant classification.

Association of SLC32A1 Missense Variants With Genetic Epilepsy With Febrile Seizures Plus.

OBJECTIVE: To identify the causative gene in a large unsolved family with genetic epilepsy with febrile seizures plus (GEFS+), we sequenced the genomes of family members, and then determined the contribution of the identified gene to the pathogenicity of epilepsies by examining sequencing data from 2,772 additional patients. METHODS: We performed whole genome sequencing of 3 members of a GEFS+ family. Subsequently, whole exome sequencing data from 1,165 patients with epilepsy from the Epi4K dataset and 1,329 Australian patients with epilepsy from the Epi25 dataset were interrogated. Targeted resequencing was performed on 278 patients with febrile seizures or GEFS+ phenotypes. Variants were validated and familial segregation examined by Sanger sequencing. RESULTS: Eight previously unreported missense variants were identified in SLC32A1, coding for the vesicular inhibitory amino acid cotransporter VGAT. Two variants cosegregated with the phenotype in 2 large GEFS+ families containing 8 and 10 affected individuals, respectively. Six further variants were identified in smaller families with GEFS+ or idiopathic generalized epilepsy (IGE). CONCLUSION: Missense variants in SLC32A1 cause GEFS+ and IGE. These variants are predicted to alter γ-aminobutyric acid (GABA) transport into synaptic vesicles, leading to altered neuronal inhibition. Examination of further epilepsy cohorts will determine the full genotype-phenotype spectrum associated with SLC32A1 variants.

BRAT1-associated neurodegeneration: Intra-familial phenotypic differences in siblings.

Recessive mutations in BRAT1 cause lethal neonatal rigidity and multifocal seizure syndrome, a phenotype characterized by neonatal microcephaly, hypertonia, and refractory epilepsy with premature death by age 2 years. Recently, attenuated disease variants have been described, suggesting that a wider clinical spectrum of BRAT1-associated neurodegeneration exists than was previously thought. Here, we report two affected siblings with compound heterozygous truncating mutations in BRAT1 and intra-familial phenotypic heterogeneity, with a less severe disease course in the female sibling. This phenotypic variability should be taken into account when treating patients with BRAT1-associated neurodegenerative disease. Mildly affected individuals with BRAT1 mutations show that BRAT1 must be considered as a cause in childhood refractory epilepsy and microcephaly with survival beyond infancy. © 2016 Wiley Periodicals, Inc.

KCNT1 mutations in seizure disorders: the phenotypic spectrum and functional effects.

Mutations in the sodium-gated potassium channel subunit gene KCNT1 have recently emerged as a cause of several different epileptic disorders. This review describes the mutational and phenotypic spectrum associated with the gene and discusses the comorbidities found in patients, which include intellectual disability and psychiatric features. The gene may also be linked with cardiac disorders. KCNT1 missense mutations have been found in 39% of patients with the epileptic encephalopathy malignant migrating focal seizures of infancy (MMFSI), making it the most significant MMFSI disease-causing gene identified to date. Mutations in KCNT1 have also been described in eight unrelated cases of sporadic and familial autosomal-dominant nocturnal frontal lobe epilepsy (ADNFLE). These patients have a high frequency of associated intellectual disability and psychiatric features. Two mutations in KCNT1 have been associated with both ADNFLE and MMFSI, suggesting that the genotype-phenotype relationship for KCNT1 mutations is not straightforward. Mutations have also been described in several patients with infantile epileptic encephalopathies other than MMFSI. Notably, all mutations in KCNT1 described to date are missense mutations, and electrophysiological studies have shown that they result in increased potassium current. Together, these genetic and electrophysiological studies raise the possibility of delivering precision medicine by treating patients with KCNT1 mutations using drugs that alter the action of potassium channels to specifically target the biological effects of their disease-causing mutation. Such trials are now in progress. Better understanding of the mechanisms underlying KCNT1-related disease will produce further improvements in treatment of the associated severe seizure disorders.

Multiplex families with epilepsy: Success of clinical and molecular genetic characterization.

OBJECTIVE: To analyze the clinical syndromes and inheritance patterns of multiplex families with epilepsy toward the ultimate aim of uncovering the underlying molecular genetic basis. METHODS: Following the referral of families with 2 or more relatives with epilepsy, individuals were classified into epilepsy syndromes. Families were classified into syndromes where at least 2 family members had a specific diagnosis. Pedigrees were analyzed and molecular genetic studies were performed as appropriate. RESULTS: A total of 211 families were ascertained over an 11-year period in Israel. A total of 169 were classified into broad familial epilepsy syndrome groups: 61 generalized, 22 focal, 24 febrile seizure syndromes, 33 special syndromes, and 29 mixed. A total of 42 families remained unclassified. Pathogenic variants were identified in 49/211 families (23%). The majority were found in established epilepsy genes (e.g., SCN1A, KCNQ2, CSTB), but in 11 families, this cohort contributed to the initial discovery (e.g., KCNT1, PCDH19, TBC1D24). We expand the phenotypic spectrum of established epilepsy genes by reporting a familial LAMC3 homozygous variant, where the predominant phenotype was epilepsy with myoclonic-atonic seizures, and a pathogenic SCN1A variant in a family where in 5 siblings the phenotype was broadly consistent with Dravet syndrome, a disorder that usually occurs sporadically. CONCLUSION: A total of 80% of families were successfully classified, with pathogenic variants identified in 23%. The successful characterization of familial electroclinical and inheritance patterns has highlighted the value of studying multiplex families and their contribution towards uncovering the genetic basis of the epilepsies.

Benign infantile seizures and paroxysmal dyskinesia caused by an SCN8A mutation.

OBJECTIVE: Benign familial infantile seizures (BFIS), paroxysmal kinesigenic dyskinesia (PKD), and their combination-known as infantile convulsions and paroxysmal choreoathetosis (ICCA)-are related autosomal dominant diseases. PRRT2 (proline-rich transmembrane protein 2 gene) has been identified as the major gene in all 3 conditions, found to be mutated in 80 to 90% of familial and 30 to 35% of sporadic cases. METHODS: We searched for the genetic defect in PRRT2-negative, unrelated families with BFIS or ICCA using whole exome or targeted gene panel sequencing, and performed a detailed cliniconeurophysiological workup. RESULTS: In 3 families with a total of 16 affected members, we identified the same, cosegregating heterozygous missense mutation (c.4447G>A; p.E1483K) in SCN8A, encoding a voltage-gated sodium channel. A founder effect was excluded by linkage analysis. All individuals except 1 had normal cognitive and motor milestones, neuroimaging, and interictal neurological status. Fifteen affected members presented with afebrile focal or generalized tonic-clonic seizures during the first to second year of life; 5 of them experienced single unprovoked seizures later on. One patient had seizures only at school age. All patients stayed otherwise seizure-free, most without medication. Interictal electroencephalogram (EEG) was normal in all cases but 2. Five of 16 patients developed additional brief paroxysmal episodes in puberty, either dystonic/dyskinetic or "shivering" attacks, triggered by stretching, motor initiation, or emotional stimuli. In 1 case, we recorded typical PKD spells by video-EEG-polygraphy, documenting a cortical involvement. INTERPRETATION: Our study establishes SCN8A as a novel gene in which a recurrent mutation causes BFIS/ICCA, expanding the clinical-genetic spectrum of combined epileptic and dyskinetic syndromes.

Mutations in the mammalian target of rapamycin pathway regulators NPRL2 and NPRL3 cause focal epilepsy.

OBJECTIVE: Focal epilepsies are the most common form observed and have not generally been considered to be genetic in origin. Recently, we identified mutations in DEPDC5 as a cause of familial focal epilepsy. In this study, we investigated whether mutations in the mammalian target of rapamycin (mTOR) regulators, NPRL2 and NPRL3, also contribute to cases of focal epilepsy. METHODS: We used targeted capture and next-generation sequencing to analyze 404 unrelated probands with focal epilepsy. We performed exome sequencing on two families with multiple members affected with focal epilepsy and linkage analysis on one of these. RESULTS: In our cohort of 404 unrelated focal epilepsy patients, we identified five mutations in NPRL2 and five in NPRL3. Exome sequencing analysis of two families with focal epilepsy identified NPRL2 and NPRL3 as the top candidate-causative genes. Some patients had focal epilepsy associated with brain malformations. We also identified 18 new mutations in DEPDC5. INTERPRETATION: We have identified NPRL2 and NPRL3 as two new focal epilepsy genes that also play a role in the mTOR-signaling pathway. Our findings show that mutations in GATOR1 complex genes are the most significant cause of familial focal epilepsy identified to date, including cases with brain malformations. It is possible that deregulation of cellular growth control plays a more important role in epilepsy than is currently recognized.

Mutations in KCNT1 cause a spectrum of focal epilepsies.

Autosomal dominant mutations in the sodium-gated potassium channel subunit gene KCNT1 have been associated with two distinct seizure syndromes, nocturnal frontal lobe epilepsy (NFLE) and malignant migrating focal seizures of infancy (MMFSI). To further explore the phenotypic spectrum associated with KCNT1, we examined individuals affected with focal epilepsy or an epileptic encephalopathy for mutations in the gene. We identified KCNT1 mutations in 12 previously unreported patients with focal epilepsy, multifocal epilepsy, cardiac arrhythmia, and in a family with sudden unexpected death in epilepsy (SUDEP), in addition to patients with NFLE and MMFSI. In contrast to the 100% penetrance so far reported for KCNT1 mutations, we observed incomplete penetrance. It is notable that we report that the one KCNT1 mutation, p.Arg398Gln, can lead to either of the two distinct phenotypes, ADNFLE or MMFSI, even within the same family. This indicates that genotype-phenotype relationships for KCNT1 mutations are not straightforward. We demonstrate that KCNT1 mutations are highly pleiotropic and are associated with phenotypes other than ADNFLE and MMFSI. KCNT1 mutations are now associated with Ohtahara syndrome, MMFSI, and nocturnal focal epilepsy. They may also be associated with multifocal epilepsy and cardiac disturbances.

Familial neonatal seizures in 36 families: Clinical and genetic features correlate with outcome.

OBJECTIVE: We evaluated seizure outcome in a large cohort of familial neonatal seizures (FNS), and examined phenotypic overlap with different molecular lesions. METHODS: Detailed clinical data were collected from 36 families comprising two or more individuals with neonatal seizures. The seizure course and occurrence of seizures later in life were analyzed. Families were screened for KCNQ2, KCNQ3, SCN2A, and PRRT2 mutations, and linkage studies were performed in mutation-negative families to exclude known loci. RESULTS: Thirty-three families fulfilled clinical criteria for benign familial neonatal epilepsy (BFNE); 27 of these families had KCNQ2 mutations, one had a KCNQ3 mutation, and two had SCN2A mutations. Seizures persisting after age 6 months were reported in 31% of individuals with KCNQ2 mutations; later seizures were associated with frequent neonatal seizures. Linkage mapping in two mutation-negative BFNE families excluded linkage to KCNQ2, KCNQ3, and SCN2A, but linkage to KCNQ2 could not be excluded in the third mutation-negative BFNE family. The three remaining families did not fulfill criteria of BFNE due to developmental delay or intellectual disability; a molecular lesion was identified in two; the other family remains unsolved. SIGNIFICANCE: Most families in our cohort of familial neonatal seizures fulfill criteria for BFNE; the molecular cause was identified in 91%. Most had KCNQ2 mutations, but two families had SCN2A mutations, which are normally associated with a mixed picture of neonatal and infantile onset seizures. Seizures later in life are more common in BFNE than previously reported and are associated with a greater number of seizures in the neonatal period. Linkage studies in two families excluded known loci, suggesting a further gene is involved in BFNE.

Single nucleotide variations in CLCN6 identified in patients with benign partial epilepsies in infancy and/or febrile seizures.

Nucleotide alterations in the gene encoding proline-rich transmembrane protein 2 (PRRT2) have been identified in most patients with benign partial epilepsies in infancy (BPEI)/benign familial infantile epilepsy (BFIE). However, not all patients harbor these PRRT2 mutations, indicating the involvement of genes other than PRRT2. In this study, we performed whole exome sequencing analysis for a large family affected with PRRT2-unrelated BPEI. We identified a non-synonymous single nucleotide variation (SNV) in the voltage-sensitive chloride channel 6 gene (CLCN6). A cohort study of 48 BPEI patients without PRRT2 mutations revealed a different CLCN6 SNV in a patient, his sibling and his father who had a history of febrile seizures (FS) but not BPEI. Another study of 48 patients with FS identified an additional SNV in CLCN6. Chloride channels (CLCs) are involved in a multitude of physiologic processes and some members of the CLC family have been linked to inherited diseases. However, a phenotypic correlation has not been confirmed for CLCN6. Although we could not detect significant biological effects linked to the identified CLCN6 SNVs, further studies should investigate potential CLCN6 variants that may underlie the genetic susceptibility to convulsive disorders.

A recurrent de novo mutation in KCNC1 causes progressive myoclonus epilepsy.

Progressive myoclonus epilepsies (PMEs) are a group of rare, inherited disorders manifesting with action myoclonus, tonic-clonic seizures and ataxia. We sequenced the exomes of 84 unrelated individuals with PME of unknown cause and molecularly solved 26 cases (31%). Remarkably, a recurrent de novo mutation, c.959G>A (p.Arg320His), in KCNC1 was identified as a new major cause for PME. Eleven unrelated exome-sequenced (13%) and two affected individuals in a secondary cohort (7%) had this mutation. KCNC1 encodes KV3.1, a subunit of the KV3 voltage-gated potassium ion channels, which are major determinants of high-frequency neuronal firing. Functional analysis of the Arg320His mutant channel showed a dominant-negative loss-of-function effect. Ten cases had pathogenic mutations in known PME-associated genes (NEU1, NHLRC1, AFG3L2, EPM2A, CLN6 and SERPINI1). Identification of mutations in PRNP, SACS and TBC1D24 expand their phenotypic spectra to PME. These findings provide insights into the molecular genetic basis of PME and show the role of de novo mutations in this disease entity.

Genetics of epilepsy: The testimony of twins in the molecular era.

OBJECTIVE: Analysis of twins with epilepsy to explore the genetic architecture of specific epilepsies, to evaluate the applicability of the 2010 International League Against Epilepsy (ILAE) organization of epilepsy syndromes, and to integrate molecular genetics with phenotypic analyses. METHODS: A total of 558 twin pairs suspected to have epilepsy were ascertained from twin registries (69%) or referral (31%). Casewise concordance estimates were calculated for epilepsy syndromes. Epilepsies were then grouped according to the 2010 ILAE organizational scheme. Molecular genetic information was utilized where applicable. RESULTS: Of 558 twin pairs, 418 had confirmed seizures. A total of 534 twin individuals were affected. There were higher twin concordance estimates for monozygotic (MZ) than for dizygotic (DZ) twins for idiopathic generalized epilepsies (MZ = 0.77; DZ = 0.35), genetic epilepsy with febrile seizures plus (MZ = 0.85; DZ = 0.25), and focal epilepsies (MZ = 0.40; DZ = 0.03). Utilizing the 2010 ILAE scheme, the twin data clearly demonstrated genetic influences in the syndromes designated as genetic. Of the 384 tested twin individuals, 10.9% had mutations of large effect in known epilepsy genes or carried validated susceptibility alleles. CONCLUSIONS: Twin studies confirm clear genetic influences for specific epilepsies. Analysis of the twin sample using the 2010 ILAE scheme strongly supported the validity of grouping the "genetic" syndromes together and shows this organizational scheme to be a more flexible and biologically meaningful system than previous classifications. Successful selected molecular testing applied to this cohort is the prelude to future large-scale next-generation sequencing of epilepsy research cohorts. Insights into genetic architecture provided by twin studies provide essential data for optimizing such approaches.

KCNT1 gain of function in 2 epilepsy phenotypes is reversed by quinidine.

OBJECTIVE: Mutations in KCNT1 have been implicated in autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and epilepsy of infancy with migrating focal seizures (EIMFS). More recently, a whole exome sequencing study of epileptic encephalopathies identified an additional de novo mutation in 1 proband with EIMFS. We aim to investigate the electrophysiological and pharmacological characteristics of hKCNT1 mutations and examine developmental expression levels. METHODS: Here we use a Xenopus laevis oocyte-based automated 2-electrode voltage clamp assay. The effects of quinidine (100 and 300 µM) are also tested. Using quantitative reverse transcriptase polymerase chain reaction, the relative levels of mouse brain mKcnt1 mRNA expression are determined. RESULTS: We demonstrate that KCNT1 mutations implicated in epilepsy cause a marked increase in function. Importantly, there is a significant group difference in gain of function between mutations associated with ADNFLE and EIMFS. Finally, exposure to quinidine significantly reduces this gain of function for all mutations studied. INTERPRETATION: These results establish direction for a targeted therapy and potentially exemplify a translational paradigm for in vitro studies informing novel therapies in a neuropsychiatric disease.

Mutations in mammalian target of rapamycin regulator DEPDC5 cause focal epilepsy with brain malformations.

We recently identified DEPDC5 as the gene for familial focal epilepsy with variable foci and found mutations in >10% of small families with nonlesional focal epilepsy. Here we show that DEPDC5 mutations are associated with both lesional and nonlesional epilepsies, even within the same family. DEPDC5-associated malformations include bottom-of-the-sulcus dysplasia (3 members from 2 families), and focal band heterotopia (1 individual). DEPDC5 negatively regulates the mammalian target of rapamycin (mTOR) pathway, which plays a key role in cell growth. The clinicoradiological phenotypes associated with DEPDC5 mutations share features with the archetypal mTORopathy, tuberous sclerosis, raising the possibility of therapies targeted to this pathway.

A variant of KCC2 from patients with febrile seizures impairs neuronal Cl- extrusion and dendritic spine formation.

Genetic variation in SLC12A5 which encodes KCC2, the neuron-specific cation-chloride cotransporter that is essential for hyperpolarizing GABAergic signaling and formation of cortical dendritic spines, has not been reported in human disease. Screening of SLC12A5 revealed a co-segregating variant (KCC2-R952H) in an Australian family with febrile seizures. We show that KCC2-R952H reduces neuronal Cl(-) extrusion and has a compromised ability to induce dendritic spines in vivo and in vitro. Biochemical analyses indicate a reduced surface expression of KCC2-R952H which likely contributes to the functional deficits. Our data suggest that KCC2-R952H is a bona fide susceptibility variant for febrile seizures.

Autosomal dominant vasovagal syncope: clinical features and linkage to chromosome 15q26.

OBJECTIVE: To establish the occurrence of an autosomal dominant form of vasovagal syncope (VVS) by detailed phenotyping of multiplex families and identification of the causative locus. METHODS: Patients with VVS and a family history of syncope were recruited. A standardized questionnaire was administered to all available family members and medical records were reviewed. Of 44 families recruited, 6 were suggestive of autosomal dominant inheritance. Genome-wide linkage was performed in family A using single nucleotide polymorphism genotyping microarrays. Targeted analysis of chromosome 15q26 with microsatellite markers was implemented in 4 families; 1 family was too small for analysis. RESULTS: Family A contained 30 affected individuals over 3 generations with a median onset of 8 to 9 years. The other families comprised 4 to 14 affected individuals. Affected individuals reported typical triggers of VVS (sight of blood, injury, medical procedures, prolonged standing, pain, frightening thoughts). The triggers varied considerably within the families. Significant linkage to chromosome 15q26 (logarithm of odds score 3.28) was found in family A. Linkage to this region was excluded in 2 medium-sized families but not in 2 smaller families. Sequence analysis of the candidate genes SLCO3A1, ST8SIA2, and NR2F2 within the linkage interval did not reveal any mutations. CONCLUSIONS: Familial VVS, inherited in an autosomal dominant manner, may not be rare and has similar features to sporadic VVS. The chromosome 15q26 locus in family A increases the susceptibility to VVS but does not predispose to a particular vasovagal trigger. Linkage analysis in the remaining families established likely genetic heterogeneity.

Mutations in PRRT2 are not a common cause of infantile epileptic encephalopathies.

Heterozygous mutations in PRRT2 have recently been identified as the major cause of autosomal dominant benign familial infantile epilepsy (BFIE), infantile convulsions with choreoathetosis syndrome (ICCA), and paroxysmal kinesigenic dyskinesia (PKD). Homozygous mutations in PRRT2 have also been reported in two families with intellectual disability (ID) and seizures. Heterozygous mutations in the genes KCNQ2 and SCN2A cause the two other autosomal dominant seizure disorders of infancy: benign familial neonatal epilepsy and benign familial neonatal-infantile epilepsy. Mutations in KCNQ2 and SCN2A also contribute to severe infantile epileptic encephalopathies (IEEs) in which seizures and intellectual disability co-occur. We therefore hypothesized that PRRT2 mutations may also underlie cases of IEE. We examined PRRT2 for heterozygous, compound heterozygous or homozygous mutations to determine their frequency in causing epileptic encephalopathies (EEs). Two hundred twenty patients with EEs with onset by 2 years were phenotyped. An assay for the common PRRT2 c.649-650insC mutation and high resolution-melt analysis for mutations in the remaining exons of PRRT2 were performed. Neither the common mutation nor any other pathogenic variants in PRRT2 were detected in the 220 patients. Our findings suggest that mutations in PRRT2 are not a common cause of IEEs.

Mutations in DEPDC5 cause familial focal epilepsy with variable foci.

The majority of epilepsies are focal in origin, with seizures emanating from one brain region. Although focal epilepsies often arise from structural brain lesions, many affected individuals have normal brain imaging. The etiology is unknown in the majority of individuals, although genetic factors are increasingly recognized. Autosomal dominant familial focal epilepsy with variable foci (FFEVF) is notable because family members have seizures originating from different cortical regions. Using exome sequencing, we detected DEPDC5 mutations in two affected families. We subsequently identified mutations in five of six additional published large families with FFEVF. Study of families with focal epilepsy that were too small for conventional clinical diagnosis with FFEVF identified DEPDC5 mutations in approximately 12% of families (10/82). This high frequency establishes DEPDC5 mutations as a common cause of familial focal epilepsies. Shared homology with G protein signaling molecules and localization in human neurons suggest a role of DEPDC5 in neuronal signal transduction.

Role of PRRT2 in common paroxysmal neurological disorders: a gene with remarkable pleiotropy.

Mutations in the gene PRRT2 encoding proline-rich transmembrane protein 2 have recently been identified as the cause of three clinical entities: benign familial infantile epilepsy (BFIE), infantile convulsions with choreoathetosis (ICCA) syndrome, and paroxysmal kinesigenic dyskinesia (PKD). Patients with ICCA have both BFIE and PKD and families with ICCA may contain individuals who exhibit all three phenotypes. These three phenotypes were all mapped by linkage analyses to the pericentromeric region of chromosome 16, and were hypothesised to have the same genetic basis due to the co-occurrence of the disorders in some families. Despite considerable effort, the gene or genes for BFIE, ICCA, and PKD were not identified for many years after the linkage region was identified. Mutations in the gene PRRT2 were identified in several Chinese families with PKD, suggesting that the gene may also be responsible for ICCA and BFIE in families linked to the chromosome 16 locus. This was demonstrated to be the case, with the majority of families with ICCA and BFIE found to have PRRT2 mutations. The vast majority of these mutations are truncating and are predicted to lead to haploinsufficiency. PRRT2 is a largely uncharacterised protein. It is expressed in the brain and has been demonstrated to interact with SNAP-25, a component of the molecular machinery involved in the release of neurotransmitters at the presynaptic membrane. Therefore, the PRRT2 protein may play a role in this process. However, the molecular mechanisms underlying the remarkable pleiotropy associated with PRRT2 mutations have still to be determined.